DONETSK, Ukraine (AFP) - The United States has warned of a "significant escalation" in the conflict between Russia and Ukraine, after Kiev announced the capture of 10 Russian paratroopers ahead of a key meeting on Tuesday between the estranged countries' leaders.
"Repeated Russian incursions into Ukraine unacceptable. Dangerous and inflammatory," US National Security Adviser Susan Rice said on Twitter late Monday.
Rice accused Russian forces of "military incursions" into Ukraine using artillery, air defense systems, tanks and troops, representing a "significant escalation" in the conflict.
"Russia has no right to send vehicles or cargo into Ukraine without Govt of Ukraine's permission," she said.
Her comments came after Kiev's security service said soldiers from the 98th airborne division based in central Russia were captured near the Ukrainian village of Dzerkalne, about 50 kilometres southeast of the rebel hub Donetsk.
'Illegal border crossing'
"Investigators opened a criminal probe into illegal border crossing by Russian armed citizens," the security service said in a statement.
Ukraine's Defence Minister Valeriy Geletey said the soldiers were captured on Monday. "Today Ukrainian armed forces captured many Russian soldiers," Geletey wrote on his Facebook page.
"Officially they are at exercises in various corners of Russia. In reality, they are participating in military aggression against Ukraine," he said. "I am addressing the relatives of Russian servicemen: find out immediately where your loved ones are. Take them out of Ukraine, where they are being forced to die."
Kiev has long accused Moscow of stoking the separatist insurgency raging in its east, but this is the first time Ukrainian authorities have claimed to take soldiers from Russia's regular army captive.
Moscow has repeatedly denied any involvement in the rebellion in Ukraine, saying any evidence pointing to this has been fabricated.
Earlier on Monday, Ukrainian military spokesman Andriy Lysenko said troops had halted a column of tanks and armoured personal carriers flying rebel flags from Russia heading towards the government-held port city of Mariupol.
But Russian Foreign Minister Sergei Lavrov dismissed the claims, saying: "There has been more than enough disinformation about our invasion. No doubt some foreign newspaper will print that 'news' tomorrow."
Meanwhile, President Petro Poroshenko on Monday dissolved Ukraine's parliament, the Verkhovna Rada, and called early elections - accusing some lawmakers of supporting the rebellion in the east that has cost some 2,200 lives in the past four months.
"Snap parliament polls are part of my peace plan," the Ukrainian leader said. "The current makeup of Verkhovna Rada supported (ousted former leader Viktor) Yanukovych," Poroshenko said, accusing lawmakers of passing "dictatorial" laws under the former Moscow-backed president.
Poroshenko and Russian President Vladimir Putin are due to attend a meeting on Tuesday between leaders of the Russian-led Customs Union and senior EU officials, including foreign policy chief Catherine Ashton, in Minsk, the capital of Belarus.
The Kremlin did not rule out Putin and Poroshenko holding direct talks, but would not confirm a bilateral meeting.
The two met briefly in France at ceremonies to mark the 70th anniversary of the D-Day landings at the beginning of June.
Officials are set to discuss the crisis as well as trade following Ukraine's signing of key political and economic agreements with the European Union in June.
The Association Agreement with the European Union opens up to Kiev the huge EU market of 500 million customers. But the talks are set to take place against a background of high tensions.
An AFP journalist witnessed heavy fighting to the south of Donetsk, the main rebel bastion in eastern Ukraine, where separatists said they had deployed fresh tanks and artillery. Explosions rang out and smoke rose from towns to the south of the city. Ukraine's military said four soldiers had been killed and 31 wounded in the past 24 hours.
The Kremlin also ratcheted up the pressure by announcing plans to send another aid convoy into eastern Ukraine "this week".
Russia unilaterally sent about 230 lorries carrying what it claimed was 1,800 tonnes of humanitarian aid to the rebel-held city of Lugansk on Friday after accusing Kiev of intentionally delaying the mission. Kiev condemned the move as a "direct invasion".
Some 400,000 people have fled their homes since April in fighting that has left residents in some besieged rebel-held cities without water or power for weeks. "We would like to agree on the conditions to send the convoy on the same route with the same participation of Ukrainian border guards and customs officers as soon as possible," Lavrov told a news conference in Moscow.
He also played down hopes for a major breakthrough in Minsk, saying only that talks would "facilitate the exchange of opinions" about "efforts to start the political process to settle the political crisis".